I've recently tried - for the first time - roasting a Kenyan peaberry (Nyeri Katarina from 2021 harvest) for the first time. It behaves extremely differently to pretty much anything else I've roasted, so I wondered what the normal approach would be.

My first attempt, I gave it much more gas early on than normal, but still ran out of momentum during 1C. Dropped earlier than planned as RoR was getting dangerously low, with only 1:12 development time. I was pretty sure that this would come out baked or underdeveloped, but it is actually pretty good. Slightly on the bland side, but quite fruity and very sweet.



After that, I gave it a more aggressive approach. Still high heat, but later gas cuts to keep the RoR up. The development was longer, and I got my planned 20F after 1C, but the roast was 1 minute shorter in total. I bumped up the air at the end to try to clear some chaff, and that seems to have affected the BT RoR curve, not sure if this is significant. Here is the curve with the first in the background:



To my surprise, this did not taste more developed, but had an aggressive acidity, that makes me think the roast was too fast.

So am I on the right lines for this type of coffee? Did I accidentally get it right first time? Are there any other approaches/techniques that I'm missing out on?

I have this same coffee and I think you are on the right track. Here's an example below that I've found has good flavor but with that zippy acidity I like in Kenyans. As for the approach, I like to hit it with heat early to build momentum, but due to the small bean size of a peaberry I back off gas a bit quicker than larger beans thru DE and Maillard. See if you can target about 15F/min heading into FCs which gives you more time in Maillard and still sufficient momentum to get good development.

I'm thinking less heat to start. Hard beans take a while to absorb heat. Too much won't get you there IME.

Thanks for all the tips. Today, tasting both as pour over (Origami/Kalita), the first roast actually tastes baked, while the second has a pleasant acidity, but without the pop that I hoped. Will have to taste these again tomorrow, maybe an immersion brew will help.

Mike - I had it in my head that harder denser beans needed more heat, and particularly early on. Maybe I'll try a profile with less extreme start-to-finish variation in the gas, to try and extend time to yellow, without running out of momentum.

I may be wrong here, but it's my understanding denser beans transmit heat internally more readily than softer beans. That said, one problem I have with denser beans is if I apply heat too slowly I find I end up chasing temps later in the roast. So generally I build momentum early with denser beans and then back off, which seems easier to control for me. (Conversely with softer beans I apply heat more slowly to avoid tipping/scorching since they don't absorb heat as well). Perhaps someone with more expertise will clarify.

mkane wrote:I'm thinking less heat to start. Hard beans take a while to absorb heat. Too much won't get you there IME.

Counterintuitive, but all things equal (like moisture content), higher density equates to faster heat transfer.

And exactly why I would start out with less heat. A dry time of less than 3minutes is ridiculous, even with an air machine.

Interesting, I'll try dropping the gas in the first stage of the roast. Hopefully that will help things. Thanks again for the help!

mkane wrote:And exactly why I would start out with less heat. A dry time of less than 3minutes is ridiculous, even with an air machine.

After a couple of experiments, this is a much more tricky task than i thought. Just decreasing the initial gas setting after the soak didn't do very much. I could reduce the drum speed, decrease airflow, increase the length of soak, close the diffuser, or some combination of the above. By using all of the above other than airflow and the diffuser, i got to around 3:30. Am i missing something? I feel like I'm probably making this much more complicated than it should be...